Surgical treatment of anterior cruciate ligament (ACL) deficiency is common, but unfortunately, no single procedure has been able to restore knee kinematics to pre-injury levels. In fact, using the International Knee Documentation committee (IKDC) guidelines, 38% of the patients were reported to have abnormal, or severely abnormal knees. Therefore, advancements in surgical ACL reconstruction, and post-operative rehabilitation to improve the outcome, would require a better understanding of the forces in the intact ACL. The broad aim of this project is to examine the in situ force and its distribution within the ACL and ACL replacement grafts under external loads, with and without muscle stabilization. It is the applicants' belief, that the intact ACL is the true "gold standard" for ACL reconstruction. Using cadaveric knees, data on both the in situ forces and knee kinematics will be obtained and used to evaluate ACL reconstruction, particularly on important variables such as graft type, number of bundles, and notchplasty. The investigators will use a newly developed robotic/universal force-moment sensor (UFS) testing system to determine the in situ forces and knee kinematics. Complex human knee motion in 6 degrees-of-freedom (DOF) will be recorded and then reproduced using a robotic manipulator. In situ forces in the intact ACL and its replacement grafts will be obtained from force data measured by the UFS. Further, this technology will yield data on the changes in knee kinematics secondary to ACL reconstruction. The same specimen can be utilized for a series of tests, allowing the intact knee joint to serve as its own control (thus minimizing interspecimen variations). It is suggested that information obtained from the proposed studies will be useful for the clinical management of ACL deficiency. It is the applicants' goal to provide data for surgeons to help them select appropriate ACL replacement grafts and reconstruction procedures, and to improve rehabilitation protocols. In the long-term, they believe that the robotic/UFS test system can be used to reproduce the knee kinematics data obtained from in vivo activities on cadaveric knees. Thus, the in situ forces and force distribution in the ACL and replacement grafts during the activities of daily living and sports could be indirectly determined.